11.3.6 The SET Type
SET is a string object that can have zero or more values, each of which must be chosen from a list of permitted values specified when the table is created.
SET column values that consist of multiple set members are specified with members separated by commas (
,). A consequence of this is that
SET member values should not themselves contain commas.
For example, a column specified as
SET('one', 'two') NOT NULL can have any of these values:
'' 'one' 'two' 'one,two'
SET column can have a maximum of 64 distinct members. A table can have no more than 255 unique element list definitions among its
SET columns considered as a group. For more information on this limit, see Limits Imposed by .frm File Structure.
Duplicate values in the definition cause a warning, or an error if strict SQL mode is enabled.
Trailing spaces are automatically deleted from
SET member values in the table definition when a table is created.
When retrieved, values stored in a
SET column are displayed using the lettercase that was used in the column definition. Note that
SET columns can be assigned a character set and collation. For binary or case-sensitive collations, lettercase is taken into account when assigning values to the column.
SET values numerically, with the low-order bit of the stored value corresponding to the first set member. If you retrieve a
SET value in a numeric context, the value retrieved has bits set corresponding to the set members that make up the column value. For example, you can retrieve numeric values from a
SET column like this:
mysql> SELECT set_col+0 FROM tbl_name;
If a number is stored into a
SET column, the bits that are set in the binary representation of the number determine the set members in the column value. For a column specified as
SET('a','b','c','d'), the members have the following decimal and binary values.
||Decimal Value||Binary Value|
If you assign a value of
9 to this column, that is
1001 in binary, so the first and fourth
SET value members
'd' are selected and the resulting value is
For a value containing more than one
SET element, it does not matter what order the elements are listed in when you insert the value. It also does not matter how many times a given element is listed in the value. When the value is retrieved later, each element in the value appears once, with elements listed according to the order in which they were specified at table creation time. Suppose that a column is specified as
mysql> CREATE TABLE myset (col SET('a', 'b', 'c', 'd'));
If you insert the values
mysql> INSERT INTO myset (col) VALUES -> ('a,d'), ('d,a'), ('a,d,a'), ('a,d,d'), ('d,a,d'); Query OK, 5 rows affected (0.01 sec) Records: 5 Duplicates: 0 Warnings: 0
Then all these values appear as
'a,d' when retrieved:
mysql> SELECT col FROM myset; +------+ | col | +------+ | a,d | | a,d | | a,d | | a,d | | a,d | +------+ 5 rows in set (0.04 sec)
If you set a
SET column to an unsupported value, the value is ignored and a warning is issued:
mysql> INSERT INTO myset (col) VALUES ('a,d,d,s'); Query OK, 1 row affected, 1 warning (0.03 sec) mysql> SHOW WARNINGS; +---------+------+------------------------------------------+ | Level | Code | Message | +---------+------+------------------------------------------+ | Warning | 1265 | Data truncated for column 'col' at row 1 | +---------+------+------------------------------------------+ 1 row in set (0.04 sec) mysql> SELECT col FROM myset; +------+ | col | +------+ | a,d | | a,d | | a,d | | a,d | | a,d | | a,d | +------+ 6 rows in set (0.01 sec)
If strict SQL mode is enabled, attempts to insert invalid
SET values result in an error.
SET values are sorted numerically.
NULL values sort before non-
mysql> SELECT * FROM tbl_name WHERE FIND_IN_SET('value',set_col)>0; mysql> SELECT * FROM tbl_name WHERE set_col LIKE '%value%';
The first statement finds rows where
set_col contains the
value set member. The second is similar, but not the same: It finds rows where
value anywhere, even as a substring of another set member.
The following statements also are permitted:
mysql> SELECT * FROM tbl_name WHERE set_col & 1; mysql> SELECT * FROM tbl_name WHERE set_col = 'val1,val2';
The first of these statements looks for values containing the first set member. The second looks for an exact match. Be careful with comparisons of the second type. Comparing set values to
' returns different results than comparing values to
'. You should specify the values in the same order they are listed in the column definition.
To determine all possible values for a
SET column, use
SHOW COLUMNS FROM and parse the
SET definition in the
Type column of the output.
In the C API,
SET values are returned as strings. For information about using result set metadata to distinguish them from other strings, see Section 27.7.4, “C API Data Structures”.